1. Field of the Invention
The present invention relates generally to telephone data communication systems, and more particularly to time independent data communication systems via non-dedicated telephone transmission lines, to remotely notify a local computer to dial out to a data network.
2. Description of the Prior Art
Various systems are presently known which provide remote notification to local computers or data sets via non-dedicated telephone transmission lines.
In the U.S. Pat. No. 4,085,292 to Leslar (1978) and U.S. Pat. No. 4,232,195 to Bartelink (1980), calls are automatically answered and tones are generated to indicate the condition of the local data set. In the U.S. Pat. No. 3,902,016 to Blouch (1975), U.S. Pat. No. 4,345,113 to Shelley (1982), and U.S. Pat. No. 5,490,210 to Sasso (1996), calls are automatically answered and tones are sensed to selectively activate devices or permit normal telephone operation. In the U.S. Pat. No. 4,086,438 to Skidmore (1978), calls are automatically answered and tones are sensed to selectively dial out to other numbers. In the U.S. Pat. No. 4,922,521 to Krikke (1990), calls are automatically answered by the local computer and the caller transmits an identification number. If the number is authorized, the line is released and the local computer dials back to the caller.
It is preferable that the call is not answered so that there is not an additional charge for the call.
In the U.S. Pat. No. 3,783,193 to Lee (1974), U.S. Pat. No. 3,876,836 to Langan (1975), U.S. Pat. No. 4,654,868 to Shelley (1987), and U.S. Pat. No. 4,995,109 to Arizumi (1991), predetermined sequences of rings are detected to selectively activate devices.
It is preferable to avoid dependence on counts of rings or sequences of rings because it is difficult to precisely determine when to hang up the remotely initiated call to cause a precise number of rings to occur on the local telephone transmission line, particularly if the mechanism is to be used with varied types of transmission line systems, such as geographically diverse public switched telephone networks.
In the U.S. Pat. No. 4,126,762 to Martin (1978), in one embodiment a predetermined time window is utilized. In another embodiment, sequential ringing signals, having a different time spacing than signals from a normal telephone call activate the local data set. In the U.S. Pat. No. 4,355,205 to Walker (1982), a coded signal is transmitted between the first and second ring. In the U.S. Pat. No. 5,361,296 to Reyes (1994), a modem is configured to sense distinctive ring types to perform selective processing of the call. In the U.S. Pat. No. 5,416,831 to Chewning (1995) and U.S. Pat. No. 5,635,980 to Lin (1997), a coded Analog Display Service Interface (ADSI) signal is sensed while the telephone is on-hook to selectively control devices.
It is preferable to avoid dependence on characteristics, such as alternative time-spacing of rings, distinctive ring types or signals sensed or transmitted while on-hook, that may not be available on all telephone transmission line systems, or may only be available at additional cost. It is also preferable that the local computer be accessible at all times, rather than only during a predetermined time window.
In the U.S. Pat. No. 4,578,534 to Shelley (1986), the data set is normally connected and the telephone is normally disconnected. The termination of the ringing signal after a predetermined number of ring bursts causes the data set to begin to communicate with the central computer. If additional ring bursts occur, a non-computer call is sensed and the data set is disconnected and the telephone connected to the telephone transmission line so that normal telephone usage is allowed.
It is preferable to connect the local computer and notification apparatus in parallel with other telephone devices to avoid the need for a particular configuration of telephone transmission line wiring.
In the U.S. Pat. No. 5,235,634 to Oliver (1993), if the number of rings counted on a particular call exceeds a predetermined number of rings, then the device is activated to seize the telephone transmission line, dial the predetermined telephone number and transmit collected data from the site over the telephone transmission line to the central host.
It is preferable to use the subscriber's existing telephone transmission line rather than install a separate dedicated line to provide access to the local device. It is preferable to avoid reliance on a maximum number of rings to avoid interfering with normal use of the subscriber's telephone. If the predetermined number of rings is small, normal telephone calls, as well as those for remote notification purpose, will trigger the device. If the predetermined number of rings is larger, and the subscriber is available, he is likely to answer a remotely initiated call intended only for notification of the local device, and his answering it may preclude the additional rings necessary for triggering the device. If the subscriber is not available but an automatic answering apparatus, such as a telephone answering machine or fax machine, is employed, it may automatically answer a remotely initiated call and preclude the additional rings necessary for triggering the device. It is also preferable to that the remotely initiated call is not answered so that there is not an additional charge for the call.
Accordingly, the need exists for a system that allows a remote notification to a local computer via non-dedicated telephone transmission lines at any time (i.e. no limitation to a time window). Furthermore, such a system should allow normal operation of the telephone. Furthermore, the remotely initiated calls and calls from outside callers should not be answered by the local computer or notification apparatus, to avoid additional charges for calls when the telephone is unanswered by the subscriber, for example. Furthermore, such a system should not rely on counts of rings or sequences of rings because it is difficult to precisely determine when to hang up the remotely initiated call to cause a precise number of rings to occur on the local telephone transmission lines, particularly if the mechanism is to be used with varied types of transmission line systems, such as geographically diverse public switched telephone networks. Furthermore, such a system should not rely on alternative time-spacing of rings, distinctive ring types or signals sensed or transmitted while on-hook, because these features may not be available to all subscribers or may only be provided at additional expense. Furthermore, the local computer and notification apparatus should connect in parallel with other telephone devices and there should be no requirement to modify the telephone transmission line wiring to the primary or secondary telephones.